Sponsored Research

Grant Award Year: 2020-2021

Principal Investigator:  Allison Roy, Environmental Conservation, University of Massachusetts Amherst

Research Description: 

Winter drawdowns are a common lake management strategy in Massachusetts that lower lake elevation during the winter to kill nuisance aquatic vegetation, among other purposes. Reservoir water elevations are altered by managing water releases from dams, resulting in increased downstream discharges during the fall and decreased discharges during the spring, relative to systems not managed for winter drawdowns. These changes in water quantity likely translate to altered habitat (e.g., bed mobilization) and water quality (e.g., temperature), with potential consequences on productivity, biotic integrity, and ecosystem health. Current state-issued guidelines for planning and permitting for winter drawdowns focus primarily on in-lake impacts and claim that “properly conducted” drawdowns should not alter flows beyond normal variation or downstream ecosystems, despite a lack of information on downstream impacts. We propose to collect continuous, high-resolution discharge and temperature data below drawdown dams and dams managed without altered discharges. These data will be used to describe variation in hydrologic and thermal regimes downstream of drawdown reservoirs and develop mechanistic hypotheses on the effects of altered flows on downstream ecosystems. Results will help managers and policy makers consider previously overlooked downstream impacts when updating management guidelines.

Report

  • Project Type: Annual Base Grant
  • ProjectID: 2020MA013B
  • Project Impact: We quantified downstream changes in hydrology and temperature in response to winter lake drawdowns in Massachusetts’ streams. We installed non-vented pressure transducers at 9 drawdown and 3 non-drawdown control sites to obtain continuous (15 min) stream discharge and temperature. In addition, we used a daily water budget to quantify the daily stream discharge alteration attributable to drawdown management. Metrics were calculated over the entire period of record, as well as during management periods of flow alteration (i.e., fall recession and spring refill), and were compared between drawdown and non-drawdown sites, as well as across a gradient of drawdown intensity. We predicted that decreased discharge during the spring lake refill period will lead to reduced flow magnitudes, reduced flow variation, and increased temperatures compared to unaltered flows, that are atypical for spring stream conditions in this region. Conversely, dam releases during fall recession were expected to increase flow magnitudes and reduce flow variation. Preliminary results show a range in hydrologic and thermal metrics across sites with different drawdown intensities (estimated based on drawdown magnitude, reservoir volume, and receiving watershed area). Despite state-wide guidelines on drawdown timing and flow rates, recession and refill were initiated at different times across sites and flow rates varied across sites. Results from this study will advance our understanding of the how drawdowns are impacting downstream hydrology and ecology, and will help inform future management practices and guidelines to minimize potential ecological impacts.
  • Does this project relate to research, outreach and engagement, or education and training? Research
  • Which of these USGS science priorities best aligns with this project: water observing; water availability; water prediction; water related emergencies and conflicts; or water-data infrastructure? Water Observing
  • Please list up to three keywords that are most relevant to this project (see keyword list provided in the instruction document): water budget, freshwater ecosystems